In recent years, hardware devices with smaller sizes and higher performance are increasingly being developed. This allows realization of systems of a plurality of different uses in a portable compact apparatus. In a single system, one or more operating systems (hereinafter, referred to as OS) are generally executed for a complete set of hardware resources such as a CPU (Central Processing Unit) and a RAM (Random Access Memory). In a compact apparatus as described above, for example, a complete set of hardware resources executing functions of a computer and a complete set of hardware resources executing functions of a cell-phone are each mounted as an independent system. Moreover, each system has a power source thereof. Also, an individual OS is executed for each system. Accordingly, two functions of a computer and a cell-phone are realized in a compact apparatus.
Incidentally, a computer is becoming increasingly capable of executing various functions alone. For example, a computer has become multimedia-capable in recent years, and a drive, an audio circuit, a sound source, speakers and the like are generally mounted thereon. Such a computer needs a lot of time after power-on until, for example, a music reproduction mechanism such as a music CD (Compact Disc) player is started up. Thus, a conventional technology to reduce the time until the startup by providing a switch to start only the music reproduction mechanism of a computer separately from the source of the computer main body is known.
When a computer and a cell-phone are realized in one system, a configuration in which a display chip (graphic chip) causing a screen of the computer and cell-phone to display is provided on the computer side only can be considered. However, when the two functions of a computer and a cell-phone are realized in one system using the above configuration, there are problems including those described below.
When an incoming call from an outside source is terminated after only the cell-phone is turned on, the compact apparatus cannot display a screen using the display chip on the computer side. Thus, for example, the user cannot check the originator's phone number of the incoming call.
If an incoming call from outside is terminated while only the cell-phone is turned on, there is a problem that it takes some time before the OS is started up even if the computer is turned on by the user at a time of the incoming call being terminated. If, on the other hand, both the cell-phone and computer are turned on in preparation for terminating processing of such an incoming call, the compact apparatus will use up batteries earlier because power consumption of particularly the computer is large.